(1) Field of the Invention
The present invention relates to a laser beam-detonatable blasting cap having improved detonatability, wherein a specifically limited explosive is used. The structure of the chamber to be charged with the explosive, the loading density of the explosive and the restraining condition for the chamber are also specifically limited.
(2) Related Art Statement
There have hitherto been used a blasting cap detonated by a safety fuse, and an electric detonator detonated by an electric current supplied through a lead wire. In addition, there has recently been developed a laser beam-detonatable blasting cap detonated by means of a laser beam.
As the laser-oscillating apparatus for such a laser beam-detonatable blasting cap, there are used a ruby laser, a YAG (yttrium.aluminum.garnet) laser and the like.
As a conventional blasting cap detonated by a laser beam generated by means of the above described laser-oscillating apparatus, there is known a blasting cap illustrated in FIG. 5 in the accompanying drawings in this specification (for further reference, see U.S. Pat. No. 3,528,372). This laser beam-detonatable blasting cap 40 comprises a vacant space 49, a first chamber 41 defined by a plate 48, and a second chamber 42, wherein an optical fiber 43 is connected through a lens 45 to the top of the explosive 46 arranged in the first chamber 41. Both the chambers 41 and 42, the plate 48, the vacant space 49, the lens 45 and the optical fiber 43 are surrounded with a restraining wall 47. The end of the optical fiber 45 is tightly closed by means of a plug 44. The explosives 46 and 50 charged into the first chamber 41 and second chamber 42, respectively, in the form of a multi-layered structure are secondary explosives. The loading density of an explosive charged in the upper portion is higher than that of an explosive charged in the lower portion in each chamber, and both the chambers are the same in the average loading density of the explosives charged therein. In FIG. 5, the numeral 51 represents a bottom plate of the blasting cap 40.
The above described laser beam-detonatable blasting cap has the following drawbacks. A secondary explosive is charged alone in the first chamber at the portion contacting the optical fiber, and therefore, a laser beam irradiated to the explosive through the optical fiber is substantially wholly reflected, and hence the laser beam is not able to be effectively absorbed in the explosive. The loading density of an explosive charged in the upper portion is higher than that of an explosive charged in the lower portion in each chamber, and therefore, the explosives charged in the first chamber are low in ignition sensitivity by the laser beam. Moreover, the restraining wall is arranged so as to surround not only the first chamber, but also the second chamber. Therefore, when the explosives in the second chamber are detonated, the power of the explosives in the second chamber is concentrated to the bottom of the second chamber, and thus, the explosives cannot effectively ignite an explosive which has been charged in the cartridge case at the portion contacting with the restraining wall.